Optimize VelocityTracker to run in linear time.

Uses a linked list for efficient pointer addition and removal.
When possible, makes use of the fact that pointer ids are usually in
sorted order to avoid quadratic time lookups when adding new data.
Fixed an incorrect assumption that the pointer count would always change
when old pointers were removed.

Also fixed a bug in InputQueue FinishedCallback recycling.

Change-Id: Ie048d3bb022d39cf4185e2fe43923a861d94c4f3